The present invention relates generally to optical frequency conversion and, more particularly, to a technique for implementing wavelength-interchanging cross-connects with wave-mixing difference frequency generation devices.
In metropolitan light-wave networks, wavelength-conversion enhances the network utilization, the connectivity, the flexibility, the ease of bandwidth management, and the reliability of network protection algorithms. Therefore wavelength conversion is an important feature of metropolitan optical networks. However, there is a need for dramatic reductions in the costs of wavelength-conversion technologies
The cost of providing wavelength-conversion can be reduced through wave mixing bulk or band conversion, where many channels at distinct frequencies are simultaneously frequency-converted, in a common device. Two native forms of wave mixing are difference-frequency generation and four-wave mixing. For both forms of conversion, an incoming channel at frequency f is converted to an outgoing channel at frequency (nxe2x88x921)xcfx80xe2x88x92f, where xcfx80 is the pump frequency, and n is the order of the wave-mixing process. We have n=2 for difference-frequency generation, and n=3 for four-wave-mixing.
With wave mixing, it is possible to build all-optical cross-connects providing non-blocking wavelength-conversion, with few converters. These architectures are multistage and comprise of many planes, and many stages of 2xc3x972 space-switches.
A Twisted Benes architecture is based on a modification of the Benes architecture with wave-mixing converters providing difference-frequency generation. It is rearrangeable and uses O(FW) wave-mixing converters. In Twisted Benes networks, for any connection, the worst case number of cascaded frequency-conversions is O(log2 W). Although it is based on bulk frequency-conversion, the Twisted Benes architecture has many limitations. First, it is only rearrangeable (i.e., some rerouting may be needed) at high load. Second, there is no cost-effective way to extend it with more planes into a strictly non-blocking network (e.g. into a Cantor network). Third, it does not offer any substantial reduction in the required number of wavelength-converters when compared to more conventional designs based on dedicated converters. Lastly, in Twisted Benes networks, for a given connection, the worst case number of cascaded frequency-conversions of O(log2 W) is large.
Other architecture of wave-mixing cross-connects have been proposed. For example, architectures have been proposed that are based on wave-mixing frequency-translation instead of difference-frequency generation. The architecture enables the design of wave-mixing nodes with any multi-log topology, where converter requirements are between O(log2 W) and O(log2 W), per stage and per plane. With this architecture, it is possible to build strictly non-blocking networks with O(F log2 W log2(FW)) wave-mixing converters overall (using a Cantor topology), instead of O(FW) wavelength-converters. However like Twisted Benes networks, these networks may suffer from large impairments, due to the large worst-case number of cascaded frequency-conversions of O(log2 W).
In view of the foregoing, it would be desirable to provide a technique for wave-mixing bulk frequency conversion which overcomes the above-described inadequacies and shortcomings. More particularly, it would be desirable to provide a technique for all-optical wavelength-conversion that uses difference-frequency generation in an efficient and cost effective manner.
According to the present invention, a technique for all-optical frequency-conversion based on wave mixing difference-frequency generation is provided. In one particular exemplary embodiment, the technique may be realized as a method for converting wavelength-channels in a network having a bxc3x97b space switch and a difference-frequency converter. The method may comprise selectively directing an incoming wavelength channel through the bxc3x97b space switch to the difference-frequency converter and converting the frequency of the incoming wavelength channel by pumping with a pump frequency of the form 2f0+{(Wxe2x88x921)xc2x1dbi}xcex94f, wherein d=0, 1, . . . , bxe2x88x921, f0 is a base frequency, W is the number of wavelengths, xcex94f is a frequency spacing between adjacent channels, and i=0, 1, . . . , logb Wxe2x88x921.
In accordance with other aspects of the invention, the technique may be realised by a method for selectively frequency translating channels in a system having W frequencies and one or more bxc3x97b space switching elements. The method may comprise selectively directing an incoming channel, operating at a respective one of the W frequencies and incoming in an incoming frequency order, based at least in part upon the respective frequency of the channel. The method may further comprise shifting the respective frequency of the selectively directed incoming channel by an amount defined by xc2x1dbixcex94f, wherein d=0, 1, . . . , bxe2x88x921, xcex94f is a frequency spacing between adjacent channels, and i=0, 1, . . . , logb Wxe2x88x921 and converting the incoming frequency order to an outgoing frequency order such that outgoing frequency order is the inverse of the incoming frequency order.
In accordance with other aspects of this exemplary embodiment of the invention, wherein the incoming channel is a first channel and the selectively directed incoming channel is a first selectively directed channel, the method may further comprise selectively directing a second channel operating at another respective one of the W frequencies based at least in part upon the respective frequency of the second channel, wherein the respective frequency of the second selectively directed channel is the same as the respective frequency of the first selectively directed channel after it has been shifted.
In accordance with other aspects of the invention the technique may comprise a method for wave-mixing bulk frequency conversion in a network, wherein the network comprises one or more stages and one or more bxc3x97b switching elements connecting a number, F, of the incoming and outgoing waveguides and, wherein the incoming and outgoing frequencies correspond to a number of wavelengths W. The method may comprise selectively directing an incoming channel operating at a respective frequency fi of the incoming frequencies and incoming on a respective waveguide xj of the incoming waveguides to a respective outgoing waveguide xjxe2x88x92d(bsxe2x88x921) of the outgoing waveguides. The method may further comprise converting the respective frequency fi to a respective outgoing frequency (f0+fWxe2x88x921)xe2x88x92fi, of the outgoing frequencies, wherein s is an index of a stage of the one or more stages, i=0, . . . , Wxe2x88x921, j=0, . . . , Fxe2x88x921, and d=zsxe2x88x92z0, where zxcfx86xe2x88x921 . . . z0 is the b-ary representation of j and xcfx86=logb F.
In accordance with other aspects of the invention the technique may comprise a method for wave-mixing bulk frequency conversion in a network, wherein the network comprises one ore more stages and one or more bxc3x97b switching elements connecting a number, F, of the incoming and outgoing waveguides and, wherein the incoming and outgoing frequencies correspond to a number of wavelengths W. The method may further comprise selectively directing a respective one of the incoming channels operating at a respective frequency fi of the incoming frequencies and incoming on a respective waveguide xj of the incoming waveguides to a respective outgoing waveguide xj+d of the outgoing waveguides and, converting the respective frequency fi to a respective outgoing frequency (f0+fWxe2x88x921+dbsxe2x88x92xcfx86xcex94f)xe2x88x92fi, of the outgoing frequencies, wherein s is an index of a stage of the one or more stages, i=0, . . . , Wxe2x88x921, j=0, . . . , Fxe2x88x921, and d=zsxe2x88x92z0, where zxcfx86xe2x88x921 . . . z0 is the b-ary representation of j, xcfx86=logb F and xcex94f is a frequency spacing.
In accordance with other aspects of the invention an apparatus is provided for converting wavelength-channels in a network having a bxc3x97b space switch and a difference-frequency converter. The apparatus may comprise a bxc3x97b space switch that selectively directs an incoming wavelength channel to a difference-frequency converter that converts the frequency of the incoming wavelength channel by pumping with a pump frequency of the form 2f0+{(Wxe2x88x921)xc2x1dbi}xcex94f, wherein d=0, 1, . . . , bxe2x88x921, f0 is a base frequency, w is the number of wavelengths, xcex94f is a frequency spacing between adjacent channels, and i=0, 1, . . . logb Wxe2x88x921.
In accordance with other aspects of the invention an apparatus is provided for selectively frequency translating channels in a system having W frequencies and one or more bxc3x97b space switching elements. The apparatus may comprise one or more bxc3x97b space switching elements that selectively direct an incoming channel operating at a respective one of the W frequencies and incoming in an incoming frequency order, based at least in part upon the respective frequency of the channel. The apparatus may further comprise a frequency shifting device that shifts the respective frequency of the selectively directed incoming channel by an amount defined by xc2x1dbixcex94f, wherein d=0, 1, . . . , bxe2x88x921, xcex94f is a frequency, spacing between adjacent channels, and i=0, 1, . . . logb Wxe2x88x921. The apparatus may further comprise a frequency order converter that converts the incoming frequency order to an outgoing frequency order such that outgoing frequency order is the inverse of the incoming frequency order.
In accordance with other aspects of this exemplary embodiment, wherein the incoming channel is a first channel and the selectively directed incoming channel is a first selectively directed channel, the one or more bxc3x97b space switching elements may also selectively direct a second channel operating at another respective one of the W frequencies based at least in part upon the respective frequency of the second channel, wherein the respective frequency of the second selectively directed channel is the same as the respective frequency of the first selectively directed channel after it has been shifted.
In accordance with other aspects of the invention an apparatus is provided for wave-mixing bulk frequency conversion in a network, wherein the network comprises one or more stages and one or more bxc3x97b switching elements connecting a number, F, of the incoming and outgoing waveguides and, wherein the incoming and outgoing frequencies correspond to a number of wavelengths W. The apparatus may comprise one or more bxc3x97b switching elements that selectively direct an incoming channel operating at a respective frequency fi of the incoming frequencies and incoming on a respective waveguide xj of the incoming waveguides to a respective outgoing waveguide xjxe2x88x92d(bsxe2x88x921) of the outgoing waveguides and, a frequency converter that converts the respective frequency fi to a respective outgoing frequency (f0=fWxe2x88x921)xe2x88x92fi, of the outgoing frequencies, wherein s is an index of a stage of the one or more stages, i=0, . . . , Wxe2x88x921, j=0, . . . , Fxe2x88x921, and d=zsxe2x88x92z0, where zxcfx86xe2x88x921 . . . z0 is the b-ary representation of j and xcfx86=logb F.
In accordance with other aspects of the invention an apparatus for wave-mixing bulk frequency conversion in a network is provided, wherein the network comprises one ore more stages and one or more bxc3x97b switching elements connecting a number, F, of the incoming and outgoing waveguides and, wherein the incoming and outgoing frequencies correspond to a number of wavelengths W. The apparatus may comprise one or more bxc3x97b switching elements that selectively direct a respective one of the incoming channels operating at a respective frequency fi of the incoming frequencies and incoming on a respective waveguide xj of the incoming waveguides to a respective outgoing waveguide Xj+d of the outgoing waveguides and, a frequency converter that converts the respective frequency fi to a respective outgoing frequency (f0+fWxe2x88x921+dbsxe2x88x92xcfx86xcex94f)xe2x88x92fi, of the outgoing frequencies, wherein s is an index of a stage of the one or more stages, i=0, . . . , Wxe2x88x921, j=0, . . . , Fxe2x88x921, and d=zsxe2x88x92z0, where zxcfx86xe2x88x921 . . . z0 is the b-ary representation of j, xcfx86=logb F and xcex94f is a frequency spacing.
The present invention will now be described in more detail with reference to exemplary embodiments thereof as shown in the appended drawings. While the present invention is described below with reference to preferred embodiments, it should be understood that the present invention is not limited thereto. Those of ordinary skill in the art having access to the teachings herein will recognize additional implementations, modifications, and embodiments, as well as other fields of use, which are within the scope of the present invention as disclosed and claimed herein, and with respect to which the present invention could be of significant utility.